Among electric vehicle driving devices, particularly, an electric vehicle driving device, which directly drives a wheel, is referred to as an in-wheel motor. Here, the in-wheel motor is a driving device that is provided near a wheel of an electric vehicle. The in-wheel motor needs to be disposed in the wheel or near the wheel. However, a relatively small space is formed in the wheel or near the wheel. Accordingly, the size of the in-wheel motor is required to be reduced.
As in-wheel motors, there are an in-wheel motor that includes a speed reducing mechanism and a direct drive type in-wheel motor that does not include a speed reducing mechanism. The in-wheel motor including the speed reducing mechanism easily ensures a rotational force, which is enough to drive an electric vehicle, when the electric vehicle starts or climbs a hill (goes up a hill). However, since the in-wheel motor including the speed reducing mechanism transmits a rotational force to a wheel through the speed reducing mechanism, the friction loss of the speed reducing mechanism occurs. The rotational speed of an output shaft of the in-wheel motor, which includes the speed reducing mechanism, is always higher than the rotational speed of the wheel. Accordingly, in the case of the in-wheel motor including the speed reducing mechanism, the loss of energy is increased by the friction loss of the speed reducing mechanism, particularly, when an electric vehicle travels at a high speed.
Meanwhile, since the direct drive type in-wheel motor transmits a rotational force to a wheel without a speed reducing mechanism, the direct drive type in-wheel motor can reduce the loss of energy. However, the direct drive type in-wheel motor cannot amplify a rotational force by the speed reducing mechanism. Accordingly, it is difficult for the direct drive type in-wheel motor to ensure a rotational force, which is enough to drive an electric vehicle, when the electric vehicle starts or climbs a hill. As a technique that ensures a rotational force enough to drive an electric vehicle, a technique, which is not an in-wheel motor but includes a speed reducing mechanism including a planetary gear mechanism and two motors, is disclosed in, for example, Patent Literature 1.